In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (see, for example, non-patent literature 1).
In the 3rd-generation mobile communication system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A)). Accordingly, in the future, it is expected that these multiple mobile communication systems will coexist, and configurations (radio base station apparatus, mobile terminal apparatus, etc.) that are capable of supporting these multiple systems will become necessary.
On the downlink of the LTE system, the CRS (Common Reference Signal), which is a cell-common reference signal, is defined. The CRS is used to demodulate data, and, besides, used to measure downlink channel quality (CQI: Channel Quality Indicator) for scheduling and adaptive control, and to measure an average downlink propagation path state for cell search and handover (mobility measurement).
On the other hand, in the downlink of a successor system of LTE (LTE-A system), in addition to the CRS, the CSI-RS (Channel State Information-Reference Signal) for dedicated use of CQI measurement is under study. The CSI-RS supports CQI measurement in a plurality of cells, taking into account data channel signal transmission/reception in coordinated multiple-point (CoMP). The CSI-RS is used for CQI measurement in neighboring cells, and, in this regard, is different from the CRS, which is used for CQI measurement in the serving cell alone.